Widely tunable cavity filter using low voltage, large out-of-plane actuation MEMS

ABSTRACT

The present application is directed to a tunable filter system. The system includes a resonator having an inner wall surrounding a cavity. The resonator includes a MEMS device positioned in the cavity including a substrate, a movable plate and a thermal actuator. The thermal actuator is has a first end coupled to the substrate and a second end coupled to the plate. The actuator moves the plate between a first and a second position in relation to the substrate. The application is also directed to a method for operating the tunable filter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/254,387 filed Nov. 12, 2015, and is also related to a applicationtitled, “MEMS DEVICE WITH LARGE OUT-OF-PLANE ACTUATION ANDLOW-RESISTANCE INTERCONNECT AND METHODS OF USE” concurrently filed,which further claims priority to U.S. Provisional Application No.62/254,380 filed on Nov. 12, 2015. The disclosures of which areincorporated herein by reference in their entirety.

BACKGROUND 1. Field

The application is directed to widely tunable cavity filters includinglarge out-of-plane MEMS.

2. Related Art

MEMS devices have different names around the world. For example, MEMS isreferred to as micromachines in Japan, or Micro Systems Technology (MST)in Europe. MEMS devices are generally less than 250 microns and involvemechanical motion. MEMS are typically fabricated employing techniquesused in the microelectronic industry, such as thin film deposition, thinfilm patterning via photolithography and reactive ion etching. MEMSdevices offer advantages including but not limited to size, weight,cost, and Quality factor (Q).

Over the last decade, there has been increased research in the field ofMEMS devices. For instance, deployment of MEMS devices has been exploredin fields including but not limited to broadband, wireless, intelligentcommunications and radar systems for commercial and militaryapplications. In particular, MEMS devices can be employed in tunableresonators that filter, for example, wideband radio frequency (RF)electromagnetic signals. These resonators generally require agilefront-end filtering. Conventional resonators, however, exhibitdiminished electrical performance with respect to its size.

What is desired in the art is a MEMS device and resonator including aMEMS device that exhibits improved electrical performance.

What is also desired in the art is a MEMS device and resonator includinga MEMS device that exhibits improved out-of-plane actuation.

What is also desired in the art is a MEMS device and resonator includinga MEMS device including fewer components resulting in smaller size andoverall reduced cost in manufacturing.

[What is further desired in the art is a MEMS device and resonator whichpromotes environmental stability.

SUMMARY

The foregoing needs are met, to a great extent, by the applicationdescribing MEMS devices, tunable resonator filters including MEMSdevices, and methods of use. The application is not limited to thesubject matter described in the Summary section and is useful forpurposes of introducing concepts explained in detail in the DetailedDescription section.

One aspect of the application is directed to a tunable filter system.The system includes a resonator having an inner wall surrounding acavity. The system also includes a MEMS device positioned in the cavity.The MEMS device includes a substrate having a first end and a second endextending along a longitudinal axis. The MEMS device also includes amovable plate having a first end and a second end. The MEMS devicefurther includes a thermal actuator having a first end coupled to thefirst end of the substrate and a second end coupled to the first end ofthe plate, the actuator moving the plate between a first and a secondposition in relation to the substrate.

In one embodiment, the resonator includes a recessed portion formed inthe inner wall of the resonator with the substrate is positioned in therecessed portion. In another embodiment, the substrate is substantiallyencapsulated in the recessed portion such that an upper surface of thesubstrate is substantially aligned with non-recessed areas of the innerwall.

In another embodiment, the resonator includes a post extending from theinner wall toward the cavity. In yet another embodiment, the MEMS devicealso includes a strap having a first end and a second end. The secondend of the strap may be coupled to the first end of the plate. In evenanother embodiment, the strap is separated from the thermal actuator bya predetermined distance that is perpendicular to the longitudinal axis.Even further, the thermal actuator extends substantially parallel to thestrap in the longitudinal axis. Yet even further, the predetermineddistance is substantially uniform between the first and second ends ofthe thermal actuator and the strap. In even another embodiment, thestrap is positioned between two thermal actuators.

In another embodiment, the filter system includes a second MEMS devicepositioned in the cavity at a predetermined distance from the MEMSdevice. The second MEMS device includes a substrate having a first endand a second end extending along a longitudinal axis. The second MEMSdevice also includes a movable plate having a first end and a secondend. The a thermal actuator having a first end coupled to the first endof the substrate and a second end coupled to the first end of the plate,the actuator moving the plate between a first position and a secondposition in relation to the substrate.

According to a second aspect of the application, a method for operatinga tunable filter is described. The method includes a step of providing aresonator including a MEMS device located in a cavity of the resonator.The MEMS device includes a substrate, movable plate and thermalactuator. In another step, the plate is actuated between a firstposition and a second position by applying electrical current to thethermal actuator. In another step, the plate is actuated between theplating between the first position and the second position by applyingelectrical power to the substrate.

In one embodiment, the plate moves about 1 mm between the first positionand the second position. In another embodiment, the step of actuatingthe plate via applying current to the thermal actuator occurs before thestep of actuating the plate via applying power to the substrate. Inanother embodiment, the plate of the MEMS device is actuated towards apost of the resonator that extends from an inner wall toward a centralarea of the cavity. In yet even another embodiment, an upper surface ofthe plate and a major surface of the post are positioned substantiallyparallel to one another and separated by a predetermined distance in thesecond position. In a further embodiment, the plate of the MEMS deviceis actuated toward a plate of a second MEMS device positioned in thecavity. In even a further embodiment, the plates of the MEMS device andthe second MEMS device are positioned substantially parallel to oneanother and separated by a predetermined distance in the secondposition.

There has thus been outlined, rather broadly, certain aspects of theapplication in order that the detailed description thereof may be betterunderstood, and in order that the present contribution to the art may bebetter appreciated. There are, of course, additional aspects of theapplication that will be described below and which will form the subjectmatter of the claims appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to facilitate a fuller understanding of the invention,reference is now made to the accompanying drawings, in which likeelements are referenced with like numerals. These drawings should not beconstrued as limiting the invention and intended only to beillustrative.

FIG. 1 illustrates a side view of a MEMS device according to anembodiment of the application.

FIG. 2 illustrates a top view of a MEMS device according to anembodiment of the application.

FIG. 3A illustrates an isometric view of a MEMS device according to anembodiment of the application.

FIG. 3B illustrates a view of a MEMS device coupled to a power sourceaccording to an embodiment of the application.

FIG. 4 illustrates a MEMS device coupled to a power source according toyet another embodiment of the application.

FIG. 5A illustrates a resonator cavity according to an embodiment of theapplication including a MEMS device.

FIG. 5B illustrates an alternative view of the resonator cavity in FIG.5A.

FIG. 6A illustrates a resonator cavity according to another embodimentof the application.

FIG. 6B illustrates an alternative view of the resonator cavity in FIG.6A.

FIG. 7A illustrates a resonator cavity according to yet anotherembodiment of the application.

FIG. 7B illustrates another view of the resonator cavity in FIG. 7A.

DETAILED DESCRIPTION

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and to the arrangements of the componentsset forth in the following description or illustrated in the drawings.The invention is capable of embodiments in addition to those describedand of being practiced and carried out in various ways. Also, it is tobe understood that the phraseology and terminology employed herein, aswell as the abstract, are for the purpose of description and should notbe regarded as limiting.

Reference in this application to “one embodiment,” “an embodiment,” “oneor more embodiments,” or the like means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the disclosure. Theappearances of, for example, the phrases “an embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment, nor are separate or alternative embodiments mutuallyexclusive of other embodiments. Moreover, various features are describedwhich may be exhibited by some embodiments and not by the other.

The use of figure numbers and/or figure reference labels in the claimsis intended to identify one or more possible embodiments of the claimedsubject matter in order to facilitate the interpretation of the claims.Such use is not to be construed as necessarily limiting the scope ofthose claims to the embodiments shown in the corresponding figures.

As used herein, “out-of-plane” deflection means the deformation is in adirection perpendicular to the largest linear dimensions of theresonator. For example, where the largest linear dimensions are indirections across a substrate surface, out-of-plane is in the verticaldirection, away from the substrate. The out-of-plane deflection isreferred to herein as “static” because it is a result of a residualstress gradient in the structural layer from which the resonator isformed. The residual film stress gradient in the structural layerinduces a strain gradient, or deflection, along the length L when theresonator is at rest.

Many radio products feature wideband frequency performance. Thesewideband radios generally require frequency agile front-end filtering.The embodiments presented for the instant application exhibit improvedelectrical performance, compact size, reduced weight, and decreasedpower.

According to the present application, it has been determined thatdevices and systems may be employed via novel MEMS architectures. Forexample, the MEMS device is configured to be both thermally andelectrostatically actuated. Electrostatic actuation can be employed tocontrol the action of very small devices, such as a microshutter andcomb-drive. The deflection of the moving electrode is controlled bythermal and/or electrostatic forces. Preferably deflection is controlledby both thermal and electrostatic forces. The moving electrode rotatesabout an axis and employs a torsional-cantilever action. In oneembodiment, the MEMS device is pushed via thermal actuation. In anotherembodiment, the MEMS device is pulled via electrostatic actuation.

The degree of out-of-plane actuation is considered large, preferablymeasuring about 1 mm or more in movement. For example, Table 1 asprovided below, describes an embodiment where applied voltage (V)affects the height (microns) of actuation of the MEMS device. Forexample, at an applied voltage of 0, the plate of the MEMS device is1,702 microns from the substrate. As voltage increases, the distancebetween the plate of the MEMS device and the substrate decreases.

TABLE 1 Voltage Current Power Resistance Height (V) (mA) (mW) (Ω) (μm) 00 0 0 1702 0.1 28.2 2.82 3.55 1700 0.2 54.7 10.94 3.66 1649 0 78.3 23.493.83 1534 0.4 98.8 39.52 4.05 1305 0.5 118.2 59.1 4.23 882 0.6 134.780.82 4.45 506 0.7 150.2 105.14 4.66 332 0.8 161.3 129.04 4.96 211

According to the application, large capacitance changes in relation tochanges in ambient temperature are envisaged. For example, a capacitorplate can be coupled to a bimorph which actuates in relation to anothercapacitor plate on a substrate. In one embodiment, the other capacitorplate may be embedded in the substrate. By so doing, large out-of-planeactuation with controlled capacitance is achieved.

According to one aspect of the application, a tunable filter isdisclosed employing large out-of-plane actuation MEMS devices. Thetunable filter is used for example, in telecommunications applicationsin view of its small weight and dimensions. In even another embodiment,the devices and systems may be employed in a wireless communicationsystem including RF-MEMS to achieve wide-band, low-loss tuning.Moreover, the systems exhibit low power, high-Q (quality factor) tunableelements.

In an embodiment, the tunable cavities of the application exhibit goodperformance resulting in a Q better than about 200 and wide tuningranges. The tunable cavity preferably is made of metal and includes aplanar substrate positioned therein. A metallic post has been machinedat the center of the cavity, which is positioned near to the tip of theMEMS cantilevers. This provides a high-Q variable capacitance. It alsoconsiderably reduces the resonator electric size.

According to an aspect of the application, as shown in FIG. 1, the MEMSdevice 100 includes a substrate 10. The substrate has a first end and asecond end extending along a longitudinal axis of the MEMS device 100.The substrate 10 may be formed from materials known in the art. In anexemplary embodiment, the substrate is substantially made of silicon.

An electrostatic actuator/sensor 20 is located on a surface of thesubstrate 10. In one embodiment, the sensor 20 is located near a secondend of the substrate 10. The electrostatic actuator/sensor 20 iscomprised of two separated layers of polysilicon. A voltage potentialdifference between the separated polysilicon layers leads to anattractive electrostatic force, bringing the two layers together. Agreater voltage potential difference generates a greater attractiveelectrostatic force and capacitance, resulting in a decrease in gapspacing between the two layers. Since the capacitance and gap spacingare highly proportional, the measured capacitance is also used to sensethe spacing between the two layers. In one embodiment, the sensor 20 maybe an electrostatic electrode.

The MEMS device 100 also includes a plate 50 having a first end and asecond end as illustrated in FIG. 1. The first end of the plate 50 isfixed to the first end of the substrate 10 via a fixation means. Thefixation means may include a clamp or a fixing plate. Meanwhile, thesecond end of the plate 50 may be substantially pulled toward the secondend of the substrate 10 via electrostatic actuation.

The plate 50 may be substantially flat in relation to a surface of thesubstrate 10 when no thermal and/or electrostatic actuations areemployed. The plate 50 can be made of materials including but notlimited to polysilicon and metal. The metals may include, for example,chrome, nickel, aluminum, titanium gold, silver and combinationsthereof. To decrease the curvature of the plate 50, the thickness isincreased by using multiple layers. The thickness of the plate 50 mayrange from about 1 to 10 microns. The thickness may preferably rangesbetween 2 and 8 microns.

The plate 50 may be made by corrugation techniques. For instance, theplate 50 may be formed by depositing alternating layers of structuralpolysilicon and sacrificial silicon oxide onto a silicon substrate 10. Afinal layer of metal may then be deposited. Acid etching of the siliconoxide after the manufacturing process completely removes the siliconoxide thus freeing the polysilicon and metal layers of the substrate 10.

The plate is electrically connected to a contact pad positioned at afirst end of the substrate 10 via a strap 60. The strap 60 extendsbetween a first end and a second end along a longitudinal axis of theMEMS device 100. The first end of the strap 60 is positioned at thefirst end of the substrate 10 and the second end of the strap 60 ispositioned adjacent to a first end of the plate 50. As shown in FIG. 3A,the strap 60 is fixed to the substrate 10 via a coupling means 310. Thecoupling means 310 may be any fixing component, such as a clamp orfixing plate, which maintains the strap 60 in a fixed position withrespect to the substrate 10.

As illustrated in FIG. 1, the thickness of the plate 50 is greater thanthe thickness of the strap 60. In another embodiment, the thickness ofthe plate 50 may be less than the thickness of the strap 60. In evenanother embodiment, the thickness of the plate 50 and strap 60 maysubstantially be the same.

In one embodiment, the second end of the strap 60 is connected to thefirst end of the plate 50. In one embodiment, the strap 60 ismechanically coupled to the plate 50. In another embodiment, the strap60 and plate 50 may form a single, unitary structure via Focused IonBeam (FIB), chemical etching, physical vapor deposition,photolithography and combinations thereof.

The strap 60 generally includes a transition metal. In one embodiment,the strap 60 may only include a single transition metal. In anotherembodiment, the transition metal may be selected from gold, chromium andcombinations thereof.

The MEMS device 100 also includes one or more thermal actuators 70. Thethermal actuators 70 as shown in FIGS. 2 and 3A are coupled to the plate50. The thermal actuators 70 may form a single, unitary structure withthe plate 50 by any known bonding technique, such as for example, viaFIB, chemical etching or combinations thereof. Alternatively, thethermal actuators 70 may be mechanically coupled to the plate 50. Forexample, as shown in FIG. 4, the plate 50 employs connectors that permitmultiple thermal actuators to be affixed thereto. As shown, the plate 50includes four connectors 455 extending from a section of each corner ofthe plate 50. Here, there are four thermal actuators 70 respectivelyconnected to the connectors 455.

The thermal actuators 70 include a first and a second end. The thermalactuators 70 generally extend between a first end of the substrate 10and a first end of the plate 50. This is shown, for example, in FIG. 3A.The first end of the thermal actuators 70 are fixed to the substrate bya coupling means 320. Coupling means 320 may be a functional equivalentof coupling 310.

In an alternative embodiment, such as in FIG. 4, first ends of thethermal actuators 70 may be fixed at various locations on the substrate10. As shown, first ends of two thermal actuators 70 are positioned at afirst end of the substrate 10. Meanwhile, first ends of two additionalthermal actuators 70 are positioned around a central portion of thesubstrate 10.

The thermal actuator 70 is comprised of polysilicon and metal, forming abimorph. Tensile and compressive stress differences between the metaland polysilicon layers introduce a curvature within the bimorph. Namely,the thermal actuator comprising a bimorph responds to changes in ambienttemperature, e.g., the thermal environment. In one embodiment, thebimorphs have two layers along with a single insulating layer. However,those skilled in the art will appreciate that the bimorph members of thepresent invention are not limited to this configuration. For example,the insulating layers may be omitted leaving only two layers ifelectrical isolation of the two layers is not desired.

According to another embodiment, the one or more thermal actuators asbimorphs have dissimilar thermal coefficients of expansion which responddifferently to thermal actuation. For example, the first layer of thebimorph may comprise a material such as gold, nickel, or anothermetallic material having a higher coefficient of expansion relative tothe material of a second layer. The second layer may comprise a materialhaving a lower coefficient of expansion relative to the material of thefirst layer, such as silicon or another suitable semiconductor material.The second layer, or silicon layer, may be split so that a current maybe passed through the silicon layer. Namely, the thermal actuators areconnected to a power source to obtain the necessary current to promoteactuation. Movement of the thermal actuators 70 causes the capacitorplates, such as the plate 50 and substrate 10, to move closer andfarther from one another. This causes a variation in the capacitance. Inan exemplary embodiment, electrostatic static actuation between anelectrode 20 on the substrate and the plate 50 may be employed to changethe spacing. This ultimately affects the capacitance.

In one embodiment, as shown in FIG. 3A, the thermal actuator 70 extendssubstantially parallel and adjacent to the strap 60. Namely, the thermalactuator 70 is spaced apart from the strap 60 by a predetermineddistance along the longitudinal axis of the MEMS device 100. In anexemplary embodiment, the strap 60 is positioned between two thermalactuators 70. The two thermal actuators 70 are spaced apart from oneanother by a predetermined distance along the longitudinal axis of theMEMS device 100. The two thermal actuators 70 are also spaced apart fromthe strap 60 by a predetermined distance. In one embodiment, thedistance between each thermal actuator 70 and the strap 60 issubstantially equivalent.

The substrate 10 may include a temperature detector 80 as illustrated inFIG. 2. Since changes in temperature affect the curvature of the thermalactuators, the ambient temperature influences the position of the plate.In another embodiment, a temperature detector is positioned on thesubstrate. The linear relationship between the change in resistance ofthe polysilicon and change in temperature permits its use fortemperature detection. The good thermal conductivity of the siliconsubstrate gives rise to near-isothermal conditions between the MEMSdevice and surrounding environment. Therefore, the calibratedresistance-to-temperature relationship in conjunction with thecalibrated temperature-to-height relationship allows for high resolutionplate position changes due to ambient temperature changes.

FIGS. 3B and 4 illustrate thermal actuators 70 electrically coupled to apower source (not shown) via leads. An electrical current passed throughthe thermal actuators 70 heats the metal and polysilicon layers byvirtue of resistive heating. The metal has a faster rate of thermalexpansion, thereby causing a decrease in curvature of the bimorph.Higher current levels induce increased resistive heating and result in agreater reduction of curvature of the bimorph.

According to another embodiment, as shown for example in FIG. 2, theMEMS device 100 includes tethers 90 operably coupled to the plate 50.The tethers 90 are comprised of polysilicon. In an embodiment, thetethers 90 connect the plate to the wafer during prior employing powerto the plate and/or substrate. An electrical current passed through thetethers 90 heats the polysilicon due to resistive heating and thetemperature increases until the tethers 90 melt. FIG. 3B illustrates thetethers in a melted state where the plate 50 is displaced from thesubstrate 10.

Another aspect of the application is directed to a method of operating aMEMS device. The method includes the step of providing a MEMS device(step 1). The MEMS device may be based upon the above-mentionedembodiments.

There is also a step of actuating the plate by applying electricalcurrent, heat or power to the thermal actuator (step 2).

Further, there is a step of actuating the plate by applying electricalcurrent/power to the substrate causing electrostatic actuation of theplate (step 3). Electrostatic forces can be employed for providing bothpull-down and attractive forces. A voltage is applied to theelectrostatic actuator/sensor that provides a potential differencebetween its separated polysilicon layers. This leads to an attractiveelectrostatic force and capacitance resulting in a decrease in spacebetween a lower face of the plate 50 and the upper face/surface of thesubstrate 10. Based upon the proportional relationship between thecapacitance and gap/space between the substrate 10 and plate 50, themeasured capacitance may also be employed to sense the spacing betweenthe separated layers.

In one embodiment, the electrical current is applied to the thermalactuator before applying current to the substrate 10. In other words,actuation resulting from the thermal actuator occurs prior to actuationresulting from the electrostatic actuator. In another embodiment, theplate 50 moves toward the substrate when greater electrical current isprovided to the thermal actuator or to the electrostatic actuator. Evenfurther, the thermal actuator may include detectors to compensate forambient temperature. Applying a current to the thermal actuator causesan increase to the spaced-apart relationship D between the sensor 20 andthe plate 50 first resulting in a desired variation of capacitancebetween them.

According to even another embodiment, the plate moves in relation to thesubstrate between a first position ‘x’ and a second position ‘x’+‘y’.The actuation distance may be up to 2 mm. According to one embodiment,the results of a tunable filter's frequency/loss versus applied voltageare shown in Table 2 below. As shown, the insertion loss graduallyincreases from about −8.50 dB to −7.42 dB between an applied voltage of0 and 0.22 volts. Moreover, the tuning frequency (GHz) increases between4.73 and 7.4 GHz during an applied voltage ranging from 0 to 0.22 volts.

TABLE 2 Voltage Tuning Frequency Insertion Loss (V) (GHz) (dB) 0 4.73−8.50 0.01 4.74 −8.53 0.02 4.74 −8.50 0.03 4.75 −8.51 0.04 4.75 −8.530.05 4.76 −8.57 0.06 4.78 −8.62 0.07 4.81 −8.52 0.08 4.83 −8.56 0.094.85 −8.68 0.1 4.89 −8.60 0.11 4.94 −8.77 0.12 4.99 −8.79 0.13 5.04−8.67 0.14 5.35 −7.92 0.15 5.83 −7.84 0.16 6.25 −7.34 0.17 6.61 −7.480.18 6.94 −7.14 0.19 7.23 −7.53 0.2 7.5 −7.24 0.21 7.75 −7.48 0.22 7.98−7.71 0.23 8.21 −7.43 0.24 8.43 −7.63 0.25 8.64 −7.87 0.26 8.81 −7.710.27 9 −7.68 0.28 9.2 −8.15 0.29 9.35 −8.32 0.3 9.51 −8.14 0.31 9.67−8.14 0.32 9.81 −8.47 0.33 9.96 −8.92 0.34 10.11 −8.95 0.35 10.22 −8.820.36 10.35 −8.86 0.37 10.46 −9.12 0.38 10.58 −9.61 0.39 10.67 −9.96 0.410.78 −10.09 0.41 10.88 −10.14 0.42 10.95 −10.20 0.43 11.04 −10.38 0.4411.12 −10.72 0.45 11.19 −11.06 0.46 11.26 −11.52 0.47 11.36 −11.91 0.4811.41 −12.24 0.49 11.59 −12.50 0.5 11.55 −12.74Tunable Cavity Filter

According to another aspect of the application, a widely tunable cavityfilter is described that uses low voltage, large out-of-plane actuationMEMS. The filter exhibits a 3:1 tuning range and is scalable todifferent frequency bands. Moreover, the filter exhibits low loss andlow power as described in Table 2 above.

Due to the cavity-based design, the filter maintains low-lossperformance and a high-Q across the entire turning range. In oneembodiment, the filter comprises at least one low voltage, largeout-of-plane actuation MEMS. The architecture of the filter usesinductive coupling as a means to couple RF energy in and out of thecavity filter.

As shown in FIG. 5A, the apparatus 500 includes a rectangularevanescent-mode cavity resonator 510 at least one low voltage,out-of-plane actuation MEMS 100. The resonator 510 includes a recessedportion 510 a formed on a first surface. The resonator 510 also includesa post 510 b that extends from a second surface toward a center of thecavity resonator 510. Preferably the first surface is positionedopposite to the second surface. In an embodiment, the post is positionedsubstantially above the recessed portion spaced apart by a predetermineddistance. Preferably, the post is substantially aligned with therecessed portion in the same plane.

The recessed portion preferably houses a substrate 10 of the MEMS 100.In one embodiment, substantially all of the substrate is positionedwithin the recessed portion 510 a. As discussed above, the MEMS device100 includes a plate 50 that is electrically coupled to a current sourcevia a thermal actuator 70. In an embodiment, the plate 50 is attached toa strap 60. The strap 60 and plate 50 are actuated via the thermalactuator 70 from a first position to a second position. The firstposition may be located a distance ‘x+y’ from the substrate 10. Thesecond position may be located a distance ‘x’ from the substrate. In oneembodiment, the predetermined distance, such as for example, ‘x+y’ maybe about 1 mm.

In one embodiment, the MEMS device 100 also includes an electrostaticactuator 30 positioned on or embedded within the substrate 20. Theelectrostatic actuator 30 is supplied with electrostatic energy via apower source to pull a plate 50 closer to the substrate 10 andelectrostatic actuator 30. The electrostatic actuator 30 may be aconductor, such as gold, chromium, platinum, polysilicon or combinationsthereof.

As depicted in FIGS. 5A-B and 6A-B, the MEMS plate 50 has a restingposition tens of microns away from the fixed post 510 b. The post 510 bis oriented. In FIG. 5A, the plate is oriented substantially parallel tothe substrate 10 that is positioned in the recessed portion 510 a. Thetop surface of the substrate 10 is flush with internal, non-recessedsurfaces of the cavity resonator 510. Tuning of the filter 500 isrealized through varying the distance between the fixed post and theplate 50. A variable capacitance is created between the fixed post 510 band the moveable plate 50. Actuating the moving plate 50 farther fromthe fixed post 510 further tunes the filter.

As shown in FIG. 6A, the post 510 b is a different width from the post510 b depicted in FIG. 5A. Moreover, MEMS device 100 includes a thermalactuator 70 having a second end that is coupled to a first end of theplate 50. The plate is actuated from a position substantially parallelto the substrate 10 to a second position that is perpendicular to thesubstrate 10 yet substantially parallel to the post 510 b. In oneembodiment, the first position is considered the resting position whenthe plate 50 is parallel to an upper surface of the substrate 50 and afloor of the cavity resonator 500. Meanwhile, the second position isconsidered the tuning or active position when the plate 50 is parallelto a main surface of the fixed post 510 b. Tuning of the filter isrealized through varying the distance between the fixed post and theMEMS plate. A variable capacitance is created between the fixed post andmoveable plate. Actuating the moveable plate farther from the fixed postfurther tunes the filter.

According to another embodiment as depicted in FIG. 7A, the resonatorcavity 510 includes two recessed portions 510 a. The recessed portions510 a are located on opposing surfaces of the resonator 510. Namely, afloor and a ceiling, respectively. Apart from the embodiments depictedin FIGS. 5 and 6, the resonator cavity 700 in FIG. 7A includes two MEMSdevices 100. The substrate 50 of each MEMS device 100 is located withinthe recessed portion 510 a of the rectangular cavity resonator 510. Eachof the MEMS devices is a low voltage, out-of-plane actuation MEMSdevice. Tuning of the filter is realized through varying the distancebetween the two moveable plates 50. A variable capacitance is createdbetween the two moveable plates 50. Actuating the moveable plates 50farther apart from one another further tunes the filter.

As depicted, one end of each plate 50 is coupled to respective thermalactuators 70. The plates 50 moves from a first position that issubstantially parallel to the upper and lower surfaces of the resonatorcavity 500. The plates 50 also move from a position that issubstantially parallel to an upper surface of the substrate. In thesecond position, the plates 50 are positioned perpendicular to the upperand lower surfaces, as well as the upper surface of the substrate 10. Inthe second position, both plates 50 are oriented substantially parallelto each other.

According to yet another embodiment, a resonator cavity 510 includingtwo MEMS devices 100 may move from a first position that issubstantially parallel to the upper and lower surfaces of the cavity 510and the upper surface of the substrate 10 to a second position that isalso substantially parallel to the upper and lower surfaces of thecavity 510 and the upper surface of the substrate. In this embodiment,the thermal actuators 70 would be longer to ensure proper tuning betweenparallel capacitor plates 50. Alternatively in one embodiment, theheight of the resonator cavity 510 may be modified to be commensuratewith the length of the thermal actuators 70 in order to ensure optimalcapacitance of the plates 50 during tuning between the first and secondpositions.

While the system and method have been described in terms of what arepresently considered to be specific embodiments, the disclosure need notbe limited to the disclosed embodiments. It is intended to cover variousmodifications and similar arrangements included within the spirit andscope of the claims, the scope of which should be accorded the broadestinterpretation so as to encompass all such modifications and similarstructures. The present disclosure includes any and all embodiments ofthe following claims.

What is claimed is:
 1. A tunable filter system comprising: a resonatorhaving an inner wall surrounding a cavity; and a MEMS device positionedin the cavity including a substrate having a first end and a second endextending along a longitudinal axis, a movable plate having a first endand a second end, and a thermal actuator having one end coupled to thefirst end of the plate, the thermal actuator moving the plate between afirst and a second position in relation to the substrate.
 2. The systemof claim 1, wherein the resonator includes a recessed portion formed inthe inner wall of the resonator, and the substrate is positioned in therecessed portion.
 3. The system of claim 2, wherein the substrate issubstantially encapsulated in the recessed portion such that an uppersurface of the substrate is substantially aligned with a non-recessedarea of the inner wall.
 4. The system of claim 1, wherein the resonatorincludes a post extending from the inner wall toward a center of thecavity.
 5. The system of claim 1, wherein the MEMS device furthercomprises: a strap having a first end and a second end, the second endof the strap being coupled to the first end of the plate.
 6. The systemof claim 5, further comprising: a second MEMS device positioned in thecavity at a predetermined distance from the MEMS device, the second MEMSdevice including a substrate having a first end and a second endextending along a longitudinal axis, a movable plate having a first endand a second end, and a thermal actuator having a first end coupled tothe first end of the substrate and a second end coupled to the first endof the plate, the actuator moving the plate between the first positionand the second position in relation to the substrate.
 7. The system ofclaim 6, wherein the plates of the MEMS device and the second MEMSdevice are configured to actuate between the first position and thesecond position, in the second position, the first and second ends ofthe plates of the MEMS device and the second MEMS device aresubstantially parallel to one another and separated by a predetermineddistance.
 8. The system of claim 5, wherein the plate of the MEMS devicemoves up to 2 mm between the first position and the second position. 9.The system of claim 5, wherein the strap is separated from the thermalactuator by a predetermined distance perpendicular to the longitudinalaxis.
 10. The system of claim 9, wherein the predetermined distance issubstantia umiform between the first and second ends of the thermalactuator and the strap.
 11. The system of claim 5, wherein the thermalactuator extends substantially parallel to the strap in the longitudinalaxis.
 12. The system of claim 5, wherein the strap is positioned betweentwo thermal actuators.
 13. A method for operating a tunable filtercomprising: providing a resonator including a MEMS device located in acavity of the resonator, the MEMS device including a substrate, movableplate and thermal actuator; actuating the plate between a first positionand a second position by applying electrical current to the thermalactuator; and actuating the plating between the first position and thesecond position by applying electrical power to the substrate.
 14. Themethod of claim 13, wherein the plate moves up to 2 mm between the firstposition and the second position.
 15. The method of claim 13, whereinthe step of actuating the plate via applying current to the thermalactuator occurs before the step of actuating the plate via applyingpower to the substrate.
 16. The method of claim 13, wherein the plate ofthe MEMS device is actuated towards a post of the resonator extendingfrom an inner wall of the resonator toward a center of the cavity. 17.The method of claim 13, wherein in the second position, an upper surfaceof the plate and a major surface of the post are positionedsubstantially parallel to one another and separated by a predetermineddistance.
 18. The method of claim 13, wherein the plate of the MEMSdevice is actuated toward a plate of a second MEMS device positioned inthe cavity.
 19. The method of claim 18, wherein the plates of the MEMSdevice and the second MEMS device are positioned substantially parallelto one another and separated by a predetermined distance in the secondposition.